When Archer was originally chosen to command NX-01, the mission apparently wasn't to deal with the dangers and opportunities of outer space: of those, Earth knew very little. Rather, the entire Warp Five project seemed to be aimed at breaking free of the real or imagined limitations imposed by the Vulcans. Starfleet wouldn't really need a peacemaker or a superb tactician for such a mission; Starfleet would need a brash adventurer who really, really hated the Vulcans and would do everything the way Vulcans never would. For that, the son of Henry Archer was the ideal choice. (And yes, him knowing his way around the Warp Five project no doubt helped, too.)
Would that sort of a person still be the ideal choice for the anti-Xindi mission? Perhaps not. But by then, Archer would have amassed unprecedented experience in dealing with outer space. And, somewhat ironically, Archer would be just about the only skipper in the Fleet who could liaise with much-needed Vulcan expertise, thanks to his unique relationship with T'Pol; no other Vulcan would have helped Earth there, and few other humans would have been helped by T'Pol.
That Archer got some peace and cooperation out of his adventures was a bit incidental. What he excelled in was poking his nose in things the Vulcans argued were off limits, asking questions Vulcans didn't want asked, and forcing aliens to
care about humans, rather than just look the other way (even if that often equated making enemies of said aliens, at least initially).
... where it took six weeks for the Enterprise to reach the expanse, the Intrepid battle group would have arrived after three or four months...
And would never catch up with the
Enterprise, because she kept on moving. There's no "battle group" if one ship is ten times faster than the rest...
Add to this the great risks of operating in the Expanse in the first place. A group of weaker ships loitering there "in support of" NX-01 would probably lead to unacceptable losses, while the "support" they offered would be negligible and any independent work they could do in studying the Xindi would be less useful still. Perhaps a support fleet floating just outside the Expanse might help - but dangers lurked even there, and e.g. the Klingons might make short work of Earth's little isolated flotilla. Earth could never send anything amounting to "force" - and doing the sensible alternative and sending "stealth" would be defeated if a useless flotilla was sent to mark the wake of the
Enterprise for the enemy.
Timo Saloniemi